This invention relates to a method for manufacturing a semiconductor module mounted with a power semiconductor device.
In inverter devices, uninterruptible power supply devices, machining equipments, industrial robots, and other equipments, semiconductor modules, which are independent of the main unit of the equipment, are employed.
As the construction of such semiconductor modules, generally, a metal base plate of prescribed thickness is used as a foundation, and a package mounted with power semiconductor devices is provided on the metal base plate (see for example Japanese Unexamined Patent Publication No. 2003-289130). For example, FIG. 7 is a schematic diagram of a semiconductor module employing a metal base plate as a foundation.
This semiconductor module 100 employs a metal base plate 101 with several millimeters in thickness as a foundation. Metal foil 103 is mounted onto the metal base plate 101 through a solder layer 102. An insulating sheet 104 is mounted onto the metal foil 103. And metal foils 105, 106 are mounted onto the insulating sheet 104. Further, on the metal foils 105, 106 are mounted semiconductor devices 109, 110, through solder layers 107, 108. Here, the semiconductor devices 109, 110 are, for example, IGBTs (Insulated Gate Bipolar Transistors), FWDs (Free Wheeling Diodes), or other devices. And, onto the semiconductor devices 109, 110 are mounted heat spreaders 113, 114, through solder layers 111, 112. A resin case 115, molded so as to surround the semiconductor devices 109, 110 and the like, is fixed onto the upper edge of the metal base plate 101.
Although not shown, metal wires, lead frames, and similar are arranged on the periphery of the semiconductor devices 109 and 110; for example, electrodes of the semiconductor devices 109, 110 are electrically mounted to a circuit pattern formed on the insulating sheet 104, or, electrical connections are formed between electrodes of the semiconductor devices 109, 110.
Further, the interior of the resin case 115 is filled with a gel 116, in order to prevent contact between metal wires and similar, and to protect the semiconductor devices 109, 110, and similar from moisture, humidity, and dust.
A cooling member 130 is positioned below the semiconductor module 100, bolts or similar are passed through holes 117 provided in the resin case 115 and metal base plate 101, and the metal base plate 101 is brought into close contact with the cooling member 130 by tightening the bolts or similar.
There are cases in which the resin case 115 is damaged in the vicinity of the holes 117 by tightening the bolts or similar. In order to prevent such damage, reinforcing metal rings 118 are provided on the inside of the holes 117 in the resin case 115.
However, such a semiconductor module 100 employs a thick metal base plate 101 as a foundation, so that the weight and size of the semiconductor module cannot be decreased.
Hence, there has been disclosed a small-size semiconductor module which does not use a metal base plate 101 as a foundation (see for example Komatsu, Saotome and Igawa, “Small-capacitance IGBT module”, Fuji Jihou, Vol. 78, No. 4, 2005, pp. 260-263).
FIG. 8 is a schematic diagram of a semiconductor module which does not use a metal base plate.
This semiconductor module 200 is based on an insulating sheet 104, metal foil 103 formed below the insulating sheet 104, and metal foils 105, 106 formed above the insulating sheet 104. Onto the metal foils 105, 106 are mounted semiconductor devices 109, 110, through solder layers 107, 108. In this type of semiconductor module 200, a resin case 115, molded so as to surround the semiconductor devices 109, 110, is fixed onto the upper edge of the insulating sheet 104. The interior of the resin case 115 is similarly filled with a gel 116 comprising a silicone material.
By means of such a semiconductor module 200, a thick metal base plate needs not be used as a foundation, so that the semiconductor module can be made lighter and more compact, and costs can be reduced.
Further, in a semiconductor module 200 of this type where there is no metal base plate, a metal hook 119 for installation is separately provided on a side portion of the resin case 115. A bolt or similar penetrates the metal hook 119, and the semiconductor module 200 is fixed to the cooling member 130 by tightening the bolt or similar.
However, in the construction of a semiconductor module 200 shown in FIG. 8, a soft gel 116, comprising a silicone material, is used as the sealing material in the resin case 115.
When a bolt is used to firmly fasten the semiconductor module 200 sealed with such a gel 116 on the cooling member 130, excessive amount of stress is applied to the insulating sheet 104 within the semiconductor module 200, and in some cases the insulating sheet 104 is damaged. That is, because the gel 116 is soft, deformation (distortion) of the insulating sheet 104 cannot be avoided. As a result, the insulating sheet 104 is damaged.
In order to avoid such damage, the semiconductor module 200 must be fastened to the cooling member 130 in such a range that there is no damage to the insulating sheet 104. Hence, in this structure of a semiconductor module 200, the metal foil 103 cannot be firmly brought into close contact with the cooling member 130. As a result, there has been a problem that an adequate cooling effect cannot be obtained.
Moreover, in the semiconductor module 200, heat is dissipated each time the semiconductor devices 109, 110 are operated, and this heat also causes deformation of the insulating sheet 104. Hence, as the semiconductor module 200 is used over a long period of time, deformation of the insulating sheet 104 repeatedly occurs. As a result, there has been a problem that the solder layers 107, 108 immediately below the semiconductor devices 109, 110 peel away.
Further, in such a semiconductor module 200, the thickness of the insulating sheet 104 is increased in order to secure adequate mechanical strength (for example, approximately 0.6 mmt or greater).
However, in a semiconductor module 200 using such a thick insulating sheet 104, there is a limit as to the thermal conductivity from the lower faces of the semiconductor devices 109, 110 to the cooling member 130. For this reason, there has been a problem that high-power semiconductor devices could not be incorporated into such semiconductor modules 200.
Also, this structure for a semiconductor module 200 necessitates the additional manufacturing step of separately installing a metal hook 119 for installation of the resin case 115.
Further objects and advantages of the invention will be apparent from the following description of the invention.